Nwankwo Kanu: Not long after helping Nigeria to an Olympic gold medal in the 1996 Atlanta Games, Kanu underwent a medical examination while at Inter Milan, which revealed a heart defect. The then 20-year-old underwent surgery to replace an aortic valve and did not return to the Serie A club until the following year. Laurence Griffiths / Getty Images

Iker Casillas and other football players to suffer cardiac-related illness – in pictures